staging: mt7621-mmc: Remove unused function msdc_dma_dump

The msdc_dma_dump function is disabled by a preprocessor macro, was
only used in the msdc_dma_setup function. The code also contains no
information about the device, it only dumps some memory for debug.

Signed-off-by: Christian Lütke-Stetzkamp <christian@lkamp.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>